http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54000
Steven Bosscher <steven at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rguenth at gcc dot gnu.org
Summary|[4.6/4.7/4.8 |[4.6/4.7/4.8 Regression]
|Regression][IVOPTS] |Performance breakdown for
|Performance breakdown for |gcc-4.{6,7} vs. gcc-4.5
|gcc-4.{6,7} vs. gcc-4.5 |using std::vector in matrix
|using std::vector in matrix |vector multiplication
|vector multiplication |(IVopts / inliner)
--- Comment #9 from Steven Bosscher <steven at gcc dot gnu.org> 2013-02-22
23:40:35 UTC ---
(In reply to comment #8)
> Thanks for the reduced testcase. The innermost loops compare as follows:
>
> 4.5:
>
> .L7:
> movsd (%rbx,%rcx), %xmm0
> addq $8, %rcx
> mulsd 0(%rbp,%rdx), %xmm0
> addq $8, %rdx
> cmpq $24, %rdx
> addsd %xmm0, %xmm1
> movsd %xmm1, (%rsi)
> jne .L7
4.8 r196182 with "--param early-inlining-insns=2" (2 x the default value):
.L13:
movsd (%rdx), %xmm0
addq $8, %rdx
mulsd (%rsi,%rax), %xmm0
addq $8, %rax
cmpq $24, %rax
addsd %xmm0, %xmm1
movsd %xmm1, 8(%rdi,%rcx)
jne .L13
>
> 4.7:
>
> .L13:
> movq 64(%rsp), %rdi
> movq 80(%rsp), %rdx
> addq %rcx, %rdi
> addq %r8, %rdx
> movsd -8(%rax,%rdi), %xmm0
> mulsd (%rsi,%rax), %xmm0
> addq $8, %rax
> cmpq $24, %rax
> addsd (%rdx), %xmm0
> movsd %xmm0, (%rdx)
> jne .L13
This is similar to what 4.8 r196182 produces without inliner tweaks:
.L18:
movq %rcx, %rdi
addq 64(%rsp), %rdi
movq %r8, %rdx
addq 80(%rsp), %rdx
movsd -8(%rax,%rdi), %xmm0
mulsd (%rsi,%rax), %xmm0
addq $8, %rax
cmpq $24, %rax
addsd (%rdx), %xmm0
movsd %xmm0, (%rdx)
jne .L18
> so we seem to have a register allocation / spilling issue here as well
> as a bad induction variable choice. GCC 4.8 is not any better here.
All true, but in the end it looks like an inliner heuristics issue first
(as also suggested by comment #3).
